Bipolar electrode lead for medical applications

ABSTRACT

A bipolar electrode lead for medical applications, such as for electrical stimulation of body tissue, has an elongated conductor extending from a source of electrical stimulation to a tissue location to which the electrical stimulation is to be delivered. The conductor is surrounded by electrical insulation. The lead has an exposed electrode tip at the tissue location. The electrical conductor is in the form of a braided hose. The electrical insulation has a gap, which exposes the braided hose conductor, at a location spaced from the electrode tip. The exposed braided conductor functions as the neutral electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a bipolar electrode lead formedical applications, particularly for use with an implantable heartpacemaker to deliver electrical stimulation pulses from circuitry withinthe pacemaker housing to a selected heart location.

2. Description of the Prior Art

The use of unipolar heart pacemaker electrode lead is known, wherein thepacemaker housing serves as the neutral electrode for the stimulationsystem. This requires that the return current path from the electrode atthe lead tip travel through the intervening body tissue between the leadtip and the pacemaker housing. It is known that this can result inunwanted muscle stimulations and/or muscle inhibitions in the tissuesurrounding the pacemaker housing.

A known solution to this problem is the use of a bipolar electrode lead,in which the neutral electrode is formed by an exposed ring ofelectrically conductive material disposed slightly spaced from theactive electrode at the tip of the lead. If the tip of the lead isdisposed, for example, inside the heart, the complete electrical currentpath will also be contained inside the heart. In order to keep thecurrent density in the neutral electrode low, the ring must have arelatively large surface area.

The relatively large dimensions of the neutral electrode in such abipolar arrangement result in considerable stiffening of the lead, whichis otherwise extremely flexible. If, for example, the tip of theelectrode lead is to be disposed in the left ventricle, the neutralelectrode will also be in the left ventricle. Given the large number ofbends to which the electrode lead is exposed, such a stiffeningrepresents a high stress, which increases the risk that damage to theinsulation, or a rupture of the conductor in the proximity of thestiffening, will occur.

If the bipolar lead is used as an atrial electrode, it can be bent intothe shape of a J, so that the tip thereof can be applied in the rightatrial appendage. Under such conditions, the neutral electrode cannot bedisposed in the region of the bent portion of the lead, because of theaforementioned stiffening problem, and also because the neutralelectrode is relatively heavy, compared to the remainder of the lead, sothat an unwanted dislocation of the anchoring of the electrode tip canoccur. If the neutral electrode is disposed at a greater distance fromthe distal end (i.e., the tip) of an atrial lead, it will come to lie inthe vena cava in most cases. If the neutral electrode is disposed atthat location, the current pulses associated with the neutral electrodecan influence the phrenic nerve, which contains sensory fibers leadingto parts of the pleura and diaphragm. Stimulation of the phrenic nervecan result in hiccups and coughing which are unpleasant for the patient.

A bipolar heart pacemaker electrode lead is described in U.S. Pat. No.4,295,270 having an electrical conductor consisting of a braided hosewhich is connected to the neutral electrode. The neutral electrode isformed by a stiff ring, so that this electrode lead has theabove-described disadvantages, despite the use of braided hose.

To make a bipolar electrode lead more elastic, a plurality of smallerneutral electrodes can be applied in succession along a portion of thelead. Such a lead is, however, relative complicated to manufacture, andis thus expensive.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a bipolar electrodelead suitable for use with an implantable heart pacemaker wherein thelead is elastic and flexible even in the region of the neutralelectrode.

The above object is achieved in accordance with the principles of thepresent invention in an electrode lead wherein at least one of theelectrically conductors is formed by a braided hose, and wherein aportion of the outer insulation is stripped away, thereby resulting in agap in the insulation through which the braided hose conductor isexposed. The exposed portion of the braided conductor functions as theneutral electrode.

The neutral electrode can thus have an arbitrarily large surface area,while continuing to remain elastic and flexible, as the remainder of theelectrode lead, without degrading the electrical properties of theelectrode lead.

In a preferred embodiment of the invention, the conductor has anelongated core, with the braided hose proceeding over at least a portionof the core. This results in the braided hose contracting when alongitudinal pulling force acts on the electrode lead, so that thebraided hose tightens around the core so that the core is not stretchedor deformed in this region. This effect can be of particular advantagefor an electrode lead wherein the core consists of a helical electricalconductor. A disadvantage of conventional leads using helical conductorsis that the helix becomes elastically or plastically stretched in anundesirable manner when such longitudinal forces act thereon. Thisdisadvantage is avoided in the present invention.

DESCRIPTION OF THE DRAWING

The single FIGURE is a side view of an electrode lead (schematicallyshortened) constructed in accordance with the principles of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the drawing, a bipolar heart pacemaker electrode lead 1constructed in accordance with the principles of the present inventionconsists of an electrode tip 3 at a distal end of the lead and anelectrode connector 4 at a proximate end of the lead, with a leadsection 2 therebetween. The connector 4 is adapted to be received in aknown manner in a mating connector of a heart pacemaker housing (notshown). The lead section 2 consists of an elongated electrical conductor5 with electrical insulation 6.

The electrode lead 1 has a further electrical conductor in the form of abraided hose 7. A section 8 of the braided hose 7 is not covered byelectrical insulation 6, thereby forming a gap in the electricalinsulation 6, so that the exposed portion 8 of the braided hose servesas the neutral electrode. This exposed portion is just as flexible asthe remainder of the lead section 2.

As can also be seen in the drawing, the electrical conductor 5, which issurrounded by the exposed portion 8 of the braided hose 7, is helical,and is preferably insulated. The braided hose 7 can proceed over theentire length of the lead section 2 to the electrode tip 3. As a result,the helical conductor 5 is supported, so that it is not significantlydeformed when a tensile force acts on the electrode lead 1.

In the exemplary embodiment shown in the drawing, the exposed portion 8of the braided hose 7 is disposed at a sufficient distance from theelectrode tip 3 to function as the neutral electrode for the electricalstimulation system. It will be understood by those skilled in the art,however that the exposed portion 8 can be arranged anywhere along thelead section 2 as may be useful for other purposes.

Although further modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventor to embody withinthe patent warranted hereon all changes and modifications as reasonablyand properly come within the scope of his contribution to the art.

I claim as my invention:
 1. A bipolar electrode lead for deliveringelectrical stimulation to a patient, said electrode lead comprising:atleast two elongated electrical conductors including an outer conductorformed by a braided hose, at least one of said conductors terminating inan active electrode adapted for exposure to body tissue of a patient toelectrically stimulate said body tissue; and insulation surrounding saidouter conductor having a gap therein exposing a portion of said braidedhose to form a flexible non-stretchable neutral electrode for saidactive electrode.
 2. A bipolar electrode lead as claimed in claim 1,wherein one of said electrical conductors forms an elongated core andwherein said conductor formed by a braided hose surrounds at least aportion of said elongated core.
 3. A bipolar electrode lead as claimedin claim 2, wherein said elongated core is a helical electricalconductor.